Vehicle engines include among other things, accessories which are driven by the engine. Accessories may include a power steering pump, an air conditioning compressor, alternator and so on. Each of these accessories has a pulley which is connected by a belt or belts to an engine crankshaft. The accessories are driven by the belt or belts as the crankshaft rotates.
In order to operate efficiently it is necessary for the belt to be placed under a certain amount of preload or tension. This may be accomplished using known methods. A moveable shaft on one of the accessories may be mechanically adjusted to tension a belt. Another method includes use of a belt tensioner.
A belt tensioner comprises a spring imparting a force upon a lever arm. The lever arm typically comprises a pulley journalled thereto. The pulley is in contact with a belt. A biasing member such as a spring in the tensioner is used to impart and maintain a belt load. The belt load is a function of the geometry of the tensioner as well as the spring rate of the tensioner spring.
Actuators have been used to control a tensioner position, and thereby a belt tension. For example they are used to adjust a phase difference between a driver and driven pulley. The control signal is derived from the relative rotational phase of a driver pulley as compared to a driven pulley.
Representative of the art is U.S. Pat. No. 5,733,214 (1998) to Shiki et al. which discloses a system for adjusting the tension of an endless transmitting belt in an internal combustion engine comprising a control system for adjusting a tension to be applied from a tensioner to an endless belt based upon a phase angle between a driver and a driven pulley.
What is needed is an automatic tensioner controlled by a belt load detected by a load cell. What is needed is an automatic tensioner responsive to an engine operating condition to control a belt tension. The present invention meets these needs.